Fix issues of unchecked return value reported by Coverity.

Fix issues of unchecked return value reported by Coverity.

CID 80926 (#2 of 2): Unchecked return value (CHECKED_RETURN)
8. check_return: Calling ForkExecAndWaitCommand without checking return value

CID 80934 (#2 of 2): Unchecked return value from library (CHECKED_RETURN)
3. check_return: Calling lseek(pkgFd, 512L, 0) without checking return value.
This library function may fail and return an error code.

CID 80927 (#4 of 4): Unchecked return value from library (CHECKED_RETURN)
5. check_return: Calling fcntl(p->stdoutFd, 4, flags | 0x800) without
checking return value. This library function may fail and return an error
code.